This invention relates to a device for localizing radiation sources.
It is particularly applicable to locating radiation sources that may be contained in a room, for example such as a high activity cell, or which may accidentally be present in a room.
A device for localizing radiation sources has previously been described in the following document which should be referred to:
(1) French patent application No. 8500088, Jan. 4 1985 (see also EP-A-0 188 973 and U.S. Pat. No. 4,797,701).
The device described in the application mentioned above localizes radiation sources by using a pinhole chamber in which a film sensitive to radiation and a film sensitive to visible light are placed in the area in which sources of radiation are likely to be located, together with a shutter that opens to take a photograph in visible light and which is transparent to radiation from sources.
The radiation sources can be localized in their environment after these films have been developed and superposed (but not in real time).
An improvement to the device described in document (1) is known by the following document which should be referred to:
(2) French patent application No. 8913281, Oct. 11, 1989 (see also EP-A-0425333 and U.S. Pat. No. 5,204,533).
A particular embodiment of the device described in this document (2) is shown diagrammatically in FIG. 1.
This device is designed to determine the location of radiation sources 2 in real time, and particulary gamma radiation sources (for example X or beta radiation).
It comprises a pinhole chamber 4 formed in a body 6 that shields chamber 4 from gamma radiation.
The shielding thus absorbs radiation from sources 2 and parasite radiation from other sources that may be outside the field.
The body 6 may be made of an appropriate material such as a tungsten based alloy known under the name xe2x80x9cDenalxe2x80x9d.
Means 8 symbolize a rotatable support of body 6 and therefore of the device.
The body 6 comprises a collimator 10 facing the chamber 4.
The wall of the collimator 10 consists of two coaxial cones with the same vertex angle, opposite each other through their common summits in which a hole is drilled to form the pinhole 12.
This collimator 10 may comprise a part 14 opaque to visible light originating from the examined area but permeable to gamma radiation, around the pinhole 12, to deal with the case in which the activity of the gamma radiation sources that are to be localized (pinhole with double diaphragm) is insufficient.
Furthermore, the collimator 10 may be interchangeable, so that a single or double diaphragm collimator can be chosen with a vertex angle appropriate to the presumed activity of the gamma sources 2 to be located.
Furthermore, changing the collimator 10 can increase or reduce the object field covered by the device, depending on the taper and focal length chosen for this collimator.
The device also comprises a mechanical shutter 16 designed to prevent visible light from the area in which the sources 2 are located, from penetrating into chamber 4, while allowing gamma radiation to pass.
This shutter 16 is a camera type iris, or for example a retractable metal plate perpendicular to the axis 18 of the chamber 4 (the axis of two cones forming the optical axis of the device) and located close to the pinhole 12 on the side of chamber 4.
Movements of the plate forming the shutter 16 are remote controlled by electromechanical means 20 themselves controlled by the remote control box 22.
This remote control box may be located at a long distance from the device if necessary.
The device also comprises a luminescent screen 24 in chamber 4 facing the pinhole 12, which is in contact with a circular shoulder inside body 6, at the same level as the bottom of the conical surface of the collimator 10.
There is a camera 26 behind screen 24 connected to real time means 28 for the acquisition, processing and displaying electrical signals output by the camera, and storage means 30.
When the shutter 16 is closed, the image of the gamma radiation sources is obtained at the end of a specific time (a few seconds, for example 10 s).
This image is stored in a first memory area of means 28.
By controlling the aperture of shutter 16, an image (in visible light) of the observed area containing the sources 2 is then obtained almost instantaneously.
This second image is also stored in the second memory area in means 28 distinct from the first memory area.
After processing of the images and particularly coloring of xe2x80x9cspotsxe2x80x9d due to the activity of sources 2 in order to clearly identify these sources and distinguish their xe2x80x9cgamma luminosityxe2x80x9d from the luminosity (in visible light) of objects present in the observed area but which do not emit any gamma radiation, the first and second images are displayed superposed on the screen of means 28, so that gamma radiation sources can be identified.
Note also that the luminescent screen 24 is transparent in the visible range and is capable of converting the gamma radiation from sources 2 reaching it through the pinhole 12 into visible radiation through camera 26 that is designed to output an image of the scene that this camera observes through the pinhole 12 (when the shutter 16 is open) in the form of electrical signals.
The entry window into the camera 26 is placed in contact with screen 24, the screen being thus placed between the pinhole 12 and the camera 26.
The choice of the screen material depends on the activity of sources to be located.
If the activity is very low, an NaI screen can be used; if it is not too strong, a bismuth germanate (BGO) screen can be used, and if the activity is strong, a scintillating plastic screen can be used, for example sufficient to detect X or beta radiation.
One possible choice, which is in no way restrictive, is to use a camera 26 of the type marketed by the LHESA company which has a sensitivity of 10xe2x88x927 lux and which comprises an image reducer with optical fibers 26a, on which the plane input face is in contact with the screen 24, this reducer being followed by an image intensifier 26b that is itself followed by a charge transfer matrix (CCD) marked in FIG. 1 as reference 26c. 
Coupling by optical fiber image reducer 26d links matrix 26c to intensifier 26b. 
An improvement to the device described in document (2) is also known in the following document, which should be referred to:
(3) French patent application No. 9403279, Mar. 21 1994 (see also EP-A-0674188 and U.S. Pat. No. 5,557,107).
This device known through document (3) comprises a collimator in front of the pinhole chamber, comprising two half-collimators free to move in rotation around a common rotation axis.
This particular collimator performs the following three functions:
easy interchangeability with the collimator,
the possibility of changing from the visible observation range to the gamma observation range (shutter), and
variation of the focal length of the collimator.
In the device shown in FIG. 1, the quality of the image in visible light depends mainly on the size of the diaphragm used for formation of this image.
This size must not be too large to prevent geometric blur, and it must not be too small to prevent blur due to diffraction.
As we have already seen, an attempt is made to optimize the image quality in visible light by using a pinhole consisting of a double diaphragm, namely a small diaphragm adapted to the formation of this visible image, and a larger diaphragm adapted to the formation of an image of radiation sources (for example gamma).
However, even after optimizing the aperture in the diaphragm, the quality of images in visible light obtained with a device of the type shown in FIG. 1 is not satisfactory.
The same is true for the device described in document (1).
The purpose of this invention is to overcome the disadvantage mentioned above by suggesting a device for localizing radiation sources capable of identifying these sources on an image of their environment in visible light, with better quality than is possible with a device of the type shown in FIG. 1 or the type described in document (1).
More precisely, the purpose of this invention is a device for localizing radiation sources that may be located in a zone, this device comprising a pinhole chamber, the wall of which acts as shielding that absorbs the said radiation, and means of closing the pinhole chamber, these closing means being transparent to source radiation, this device also comprising means of forming images in the pinhole chamber facing this pinhole, in order to obtain firstly an image of the sources due to their radiation and secondly an image of the area due to visible light from this area when the shutter is open, this device being characterized in that some of the shielding in which the pinhole is located is free to move and is fixed to an optical system that produces sharp images in visible light on the required field depth, this optical system being capable of substituting itself for the pinhole to create an image of the area, and vice versa to form an image of the sources.
The magnification of the optical system should be exactly the same as the magnification of the pinhole forming the image of the sources.
According to one preferred embodiment of the device according to the invention, the mobile part of the shielding and the optical system are free to move in rotation about an axis parallel to the center line or the chamber.
Preferably, the shape of the moving part of the shielding is appropriate for exactly reconstituting the wall of the pinhole chamber when this pinhole is in the position in which the image of the sources can be formed.
The device may also comprise a motor reduction gear assembly fixed to the wall of the chamber, and outside the chamber, and designed to rotate the assembly formed by the mobile part of the shielding and the optical system around the axis parallel to the axis of the chamber.
Preferably, the optical system comprises:
two lenses, designed to control focusing on the image formation means, and
a diaphragm placed between the two lenses, the aperture of which is selected so as to obtain the required field depth.
The diameter of this aperture or pupil, which controls the aperture of the optical system, should be optimized firstly to maximize the aperture of this optical system and secondly to obtain perfect focusing of the image within the required range of field depths (for example 1 m to 10 m).
The closing means may comprise a mobile shutter transparent to radiation from sources and placed between the image formation means and the moving part of the shielding.
However, in one preferred embodiment that is easier to make, these closing means comprise an element that is opaque to visible light and transparent to radiation from sources and which permanently closes the pinhole.
The pinhole chamber closing means that are transparent to radiation from sources are preferably composed of a material chosen such that it minimizes attenuation of the sources.
For example, thin aluminum and beryllium could be used for the gamma radiation.
According to a first particular embodiment of the device according to the invention, the image formation means comprise a luminescent screen, transparent in the visible range and capable of converting radiation from the sources into visible light radiation, the shutter means also being capable of preventing visible light from the area from reaching the screen, the device also comprising a camera that is optically coupled to the screen and which is capable of supplying an image of the sources in the form of electric signals by means of light radiation that it receives from the screen, and an image of the area by means of visible light that it receives from this area through the screen when the shutter means are open.
According to a second particular embodiment, the image formation means comprise a device with two films, one of these two films being sensitive to radiation from sources and the other to visible light from the area.